Lubricant composition and lubricant composition-covered metal sheet

ABSTRACT

Provided is a lubricant composition and a lubricant composition-covered metal sheet excellent in degreasing property corrosion resistance, and moldability of a metal sheet. 
     The lubricant composition of the invention comprises a paraffin wax, a liquid paraffin, and a sorbitan fatty acid ester, with a content of the liquid paraffin relative to 100 parts by mass of the paraffin wax being 10-500 parts by mass; an HLB value of the sorbitan fatty acid ester being more than 0 and 4.5 or less; and a content of the sorbitan fatty acid ester relative to 100 parts by mass of total of the paraffin wax and the liquid paraffin being 5-30 parts by mass. The sorbitan fatty acid ester preferably has a sorbitan having only a part of hydroxyl groups thereof esterified. The lubricant composition preferably further comprises a polyoxyethylene alkyl ether which preferably has an HLB value of 10-20.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lubricant composition and a lubricant composition-covered metal sheet.

2. Description of the Related Art

Conventionally, in a presswork of a metal sheet, lubricant oil has been applied on the metal sheet in order to reduce damages of a die or of a surface of the metal sheet due to an insufficient lubrication. However, when a lubricant oil is used in this way in an aluminum alloy sheet or the like, an aluminum soap is formed from fatty acid or fatty oil in the lubricant oil, due to a heat at the time of presswork, causing a problem of discoloration, corrosion, or insufficient degreasing, which make the presswork difficult. There is also a problem that, in a washing of a lubricant oil, an organic solvent volatilizes and pollutes a work environment.

Therefore, there has been developed a technique of calcining a liquid lubricant composition after applied on a metal sheet, to form a solid lubricant layer (see publication of JP 2011-005425 A). This lubricant layer comprises an alkaline degreasing urethane resin in addition to the lubricant composition, and is removed by alkali after the metal sheet is pressed.

However, in this technique, removal of the coating after the pressing tends to be insufficient, and a lubricant composition tends to be left on a surface of a metal sheet. In addition, the lubricant layer is easily deteriorated as time passes after the lubricant layer is formed, and has an insufficient corrosion resistance. Moreover, since the technique uses lubricant oil together with the lubricant layer, the above described deterioration of moldability due to a lubricant oil cannot be sufficiently prevented.

SUMMARY OF THE INVENTION Technical Problem

The present invention has been made in view of the above described circumstances, and object of the present invention is to provide a lubricant composition which is excellent in degreasing property, corrosion resistance, and moldability of a metal sheet, and a lubricant composition-covered metal sheet.

Solution to Problem

The invention which has been made in order to solve the above described problem is a lubricant composition comprising a paraffin wax, a liquid paraffin, and a sorbitan fatty acid ester, which is characterized in that content of the liquid paraffin relative to 100 parts by mass of the paraffin wax is 10 parts by mass or more and 500 parts by mass or less, HLB value of the sorbitan fatty acid ester is 4.5 or less and more than 0, and content of the sorbitan fatty acid ester elative to 100 parts by mass of total of the paraffin wax and the liquid paraffin is 5 parts by mass or more and 30 parts by mass or less.

By comprising the paraffin wax and the liquid paraffin at the above described proportion, the lubricant composition improves a friction reducing effect at the time of pressing, and as a result, improves the moldability of a metal sheet covered with the lubricant composition. In addition, the degreasing property by alkali of the lubricant composition is also improved. Furthermore, by comprising the sorbitan fatty acid ester having an HLB value in the above described range at the above described proportion, the lubricant composition is capable of improving the corrosion resistance thereof, due to a low hydrophilicity of the sorbitan fatty acid ester.

The sorbitan fatty acid ester is preferably one comprising a sorbitan having only a part of hydroxyl groups thereof esterified. When the sorbitan fatty acid ester is one comprising a sorbitan having only a part of hydroxyl groups thereof esterified, the mixing of the paraffin wax and the liquid paraffin become still easier, and it is possible to further improve the degreasing property.

It is preferred that the composition further comprises a polyoxyethylene alkyl ether, and an HLB value of this polyoxyethylene alkyl ether is preferably 10 or more and 20 or less. When the lubricant composition comprises a polyoxyethylene alkyl ether having an HLB value in the above range, permeation of a degreasing liquid into the lubricant composition is enhanced, and as a result, it is possible to further improve the degreasing property.

It is preferred that a total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether relative to 100 parts by mass of total of the paraffin wax and the liquid paraffin is 5 parts by mass or more and 40 parts by mass or less. By controlling the total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether to the above range, it is possible to provide the degreasing property, the corrosion resistance, and the moldability of a metal sheet covered with the lubricant composition at high levels together.

It is preferred that the paraffin wax has a melting point determined in conformity with JIS-K2235 (2009) of 45° C. or higher and 65° C. or lower. By controlling the melting point of the paraffin wax to the above range, it is possible to further improve the degreasing property.

It is preferred that a molecular weight of the liquid paraffin is larger than a molecular weight of the paraffin wax, and a difference between the molecular weight of the liquid paraffin and the molecular weight of the paraffin wax is preferably 50 or more and 200 or less. When the difference of the molecular weights is in the above range, it is possible to provide the degreasing property and the moldability of a metal sheet covered with the lubricant composition at high levels together.

At the same time, the invention which has been made in order to solve the above described problem is a lubricant composition-covered metal sheet comprising a metal sheet and a lubricant layer laminated at least on one of the faces of the metal sheet, characterized in that the lubricant layer is formed with the lubricant composition.

For using the lubricant composition, the lubricant composition-covered metal sheet is excellent in degreasing property and corrosion resistance, and at the same time, excellent in moldability in a presswork.

As used herein, the “HLB (Hydrophile-Lipophile Balance) value” refers to an index which represents a ratio of relative affinities of a surfactant in an oil-water system to each liquid, meaning an HLB value at 25° C. as defined in J. Soc. Cosm. Chem., 1954, 5: p249-256, for example, obtained by the following formula: a molecular weight of a hydrophilic group portion/a molecular weight of a surfactant×100/5″. The “molecular weight” refers to a number average molecular weight which is found on the basis of a molecular weight distribution obtained by a Gel Permeation Chromatography (GPC).

Effects of the Invention

The lubricant composition and the lubricant composition-covered metal sheet are excellent in degreasing property and corrosion resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, a lubricant composition and a lubricant composition-covered metal sheet according to the present invention will be described in detail.

[Lubricant Composition]

The lubricant composition comprises a paraffin wax, a liquid paraffin, and a sorbitan fatty acid ester. The lubricant composition may further comprise a polyoxyethylene alkyl ether as an optional component. Furthermore, the lubricant composition may comprise other component such as a wax other than paraffin waxes, a higher fatty acid, a higher alcohol, fine particles of a resin, an organic peroxide, a solvent, etc.

The lubricant composition is preferably solid in a normal temperature (for example, 25° C.). By being solid, the lubricant composition is easily applied uniformly onto a metal sheet.

In a case that the lubricant composition has a fluidity, a lower limit of a viscosity at 25° C. of the lubricant composition is preferably 50 Pa's, and more preferably 100 Pa's. When the viscosity is smaller than the lower limit, there is a concern that the fluidity of the lubricant composition is excessively increased, and as a result, handling of the lubricant composition in covering a metal sheet becomes complicated. As used herein, the “viscosity” refers to a value determined in conformity with JIS-Z8803 (2011).

<Paraffin Wax>

The paraffin wax is a wax comprising a straight-chain saturated hydrocarbon as a main component, having a number of carbon atoms of 20 to 48, which is solid in a normal temperature. This paraffin wax provides a friction reducing effect superior to those provided by generally used lubricant oils, and prevents a metal sheet from being damaged at pressing. Besides, the paraffin wax is capable of improving the viscosity of the lubricant composition to solidify the lubricant composition at a normal temperature. On the other hand, the paraffin wax itself has a characteristic that a degreasing is difficult in a low temperature degreasing liquid, for having a high crystallinity which makes a molecular motion hard to occur. However, by addition of a liquid paraffin and a sorbitan fatty acid ester, it is possible to improve the degreasing property, with keeping a moldability of a metal sheet.

The paraffin wax comprises n-paraffin as a main component, and may further comprise a small amount of i-paraffin, naphthene, etc. As the paraffin wax, those generally on the market may be used. As used herein, the “main component” refers to a component contained in the largest amount in terms of mass, for example, a component contained in an amount of 50 mass % or more.

A lower limit of a melting point determined in conformity with JIS-K2235 (2009) of the paraffin wax is preferably 45° C., and more preferably 47° C. On the other hand, an upper limit of the melting point is preferably 60° C., and more preferably 50° C. When the melting point is lower than the lower limit, there is a concern that it becomes difficult to solidify the lubricant composition at a normal temperature (for example, 25° C.). To the contrary, when a melting point exceeds the upper limit, there is a concern that the degreasing property of the lubricant composition is lowered.

An upper limit of a melting point of the paraffin wax is preferably +10° C., and more preferably +5° C. to a temperature of a degreasing liquid used in a degreasing. When the melting point exceeds the upper limit, there is a concern that the degreasing property of the lubricant composition is lowered.

An upper limit of a molecular weight of the paraffin wax is preferably 400, and more preferably 390. On the other hand, a lower limit of the molecular weight is preferably 300, and more preferably 350. When the molecular weight is smaller than the lower limit, there is a concern that it becomes difficult to solidify the lubricant composition at a normal temperature (for example, 25° C.). To the contrary, when the molecular weight exceeds the upper limit, there is a concern that the degreasing property of the lubricant composition is lowered.

<Liquid Paraffin>

Liquid paraffin is generally used as a general term for those which comprise a mixture of chain saturated hydrocarbons having a number of carbon atoms of 20 or more as a main component, and are liquid in a normal temperature. A liquid paraffin improves lubrication of the lubricant composition, improves compatibility of the lubricant composition as a whole, and controls the viscosity of the lubricant composition to the above range. Furthermore, for comprising the liquid paraffin, the lubricant composition is excellent in degreasing property. As the liquid paraffin, those generally on the market may be used.

A lower limit of a density of the liquid paraffin is preferably 0.6 g/cm³, and more preferably 0.7 g/cm³. On the other hand, an upper limit of the density is preferably 1.0 g/cm³, and more preferably 0.9 g/cm³. When the density is smaller than the lower limit, there is a concern that a corrosion resistance of the lubricant composition is lowered. To the contrary, when the density exceeds the upper limit, there is a concern that the degreasing property of the lubricant composition is lowered.

A lower limit of a kinematic viscosity of the liquid paraffin is preferably 15 mm²/s, more preferably 20 mm²/s, and even more preferable 30 mm²/s. On the other hand, an upper limit of the kinematic viscosity is preferably 80 mm²/s, more preferably 70 mm²/s, and even more preferably 60 mm²/s. When the kinematic viscosity is lower than the lower limit, there is a concern that moldability of a metal sheet covered with the lubricant composition is lowered. To the contrary, when the kinematic viscosity exceeds the upper limit, there is a concern that the lubricant composition is softened excessively, resulting in a peeling or a damage of the lubricant composition after applied on a metal sheet. As used herein, the “kinematic viscosity” refers to a value determined at 40° C. in conformity with JIS-K2283 (2000).

A lower limit of a molecular weight of the liquid paraffin is preferably 250, more preferably 300, and even more preferably 400. On the other hand, an upper limit of the molecular weight is preferably 600, more preferably 500, and even more preferably 480. When the molecular weight is smaller than the lower limit, there is a concern that a strength of a coating formed with the lubricant composition is lowered. To the contrary, when the molecular weight exceeds the upper limit, there is a concern that the degreasing property of the lubricant composition is lowered.

It is preferred that a molecular weight of the liquid paraffin is larger than a molecular weight of the paraffin wax, and a lower limit of a difference between the molecular weight of the liquid paraffin and the molecular weight of the paraffin wax is preferably 50, and more preferably 55. On the other hand, an upper limit of the difference between the molecular weights is preferably 200, and more preferably 190. When the difference between the molecular weights is smaller than the lower limit, there is a concern that it becomes difficult for the lubricant composition to provide both the degreasing property and the moldability of a metal sheet covered with the lubricant composition. To the contrary, when the difference between the molecular weights exceeds the upper limit, there is a concern that it becomes difficult to mix the liquid paraffin and the paraffin wax.

A lower limit of a content of the liquid paraffin relative to 100 parts by mass of the paraffin wax is preferably 10 parts by mass, more preferably 50 parts by mass, and even more preferably 80 parts by mass. On the other hand, an upper limit of the content is 500 parts by mass, preferably 200 parts by mass, and even more preferably 150 parts by mass. When the content is smaller than the lower limit, there is a concern that the degreasing property of the lubricant composition is lowered. To the contrary, when the content exceeds the upper limit, there is a concern that it becomes difficult to solidify the lubricant composition at a normal temperature.

A lower limit of total content of the paraffin wax and the liquid paraffin in the lubricant composition is preferably 70 mass %, and more preferably 75 mass %. On the other hand, an upper limit of the total content is preferably 95 mass %, and more preferably 90 mass %. When the total content is lower than the lower limit, there is a concern that moldability of a metal sheet covered with the lubricant composition is lowered. To the contrary, when the total content exceeds the upper limit, there is a concern that content of the sorbitan fatty acid ester goes short, and as a result, it becomes difficult to mix the paraffin wax and the liquid paraffin.

<Sorbitan Fatty Acid Ester>

A sorbitan fatty acid ester is generally used as a surfactant. For having a low hydrophilicity, a sorbitan fatty acid ester contributes to a mixing of the paraffin wax and the liquid paraffin, and also contributes to a mixing of a compound having a high hydrophilicity such as a polyoxyethylene alkyl ether which will be described later and a paraffin wax or the like having a high hydrophobicity. When the lubricant composition comprises the sorbitan fatty acid ester, an affinity between a degreasing liquid and the lubricant composition is improved, and the degreasing property of the lubricant, composition is improved.

Examples of the sorbitan fatty acid ester may include those which comprise a sorbitan having only a part of hydroxyl groups thereof esterified.

Examples of those which comprise a sorbitan having only a part of hydroxyl group thereof esterified may include sorbitan monocaprylate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan mono-oleate, sorbitan sesquioleate, sorbitan trioleate, sorbitan mono-isostearate, sorbitan sesquiisostearate, etc. Among them, sorbitan trioleate is preferred. When the sorbitan fatty acid ester is such one comprising a sorbitan having only a part of hydroxyl groups thereof esterified, the mixing of the paraffin wax and the liquid paraffin becomes still easier, and at the same time, it is possible to further improve the degreasing property.

The sorbitan fatty acid ester is preferably a tri-ester having three of hydroxyl groups thereof esterified. When the sorbitan fatty acid ester is the tri-ester, it is possible to further lower the hydrophilicity of the sorbitan fatty acid ester, and as a result, the corrosion resistance of the lubricant composition is further improved.

An HLB value of the sorbitan fatty acid ester is preferably more than 0. A lower limit of the HLB value is preferably 0.5, and more preferably 0.8. On the other hand, an upper limit of the HLB value is 4.5, preferably 4, more preferably 3, and even more preferably 2. When the HLB value is lower than the lower limit, there is a concern that cost of the sorbitan fatty acid ester increases. To the contrary, when the HLB value exceeds the upper limit, there is a concern that the hydrophilicity of the lubricant composition is increased, resulting in a lowering of the corrosion resistance.

A lower limit of a content of the sorbitan fatty acid ester relative to 100 parts by mass of total of the paraffin wax and the liquid paraffin is 5 parts by mass, preferably 7 parts by mass, more preferably 9 parts by mass, and even more preferably 10 parts by mass. On the other hand, an upper limit of the content is 30 parts by mass, preferably 25 parts by mass, more preferably 23 parts by mass, and even more preferably 20 parts by mass. When the content is smaller than the lower limit, there is a concern that the paraffin wax and the liquid paraffin are not sufficiently mixed. To the contrary, when the content exceeds the upper limit, there is a concern that moldability of a metal sheet covered with the lubricant composition is lowered.

<Polyoxyethylene Alkyl Ether>

A polyoxyethylene alkyl ether is generally used as a surfactant. For having a high hydrophilicity, a polyoxyethylene alkyl ether improves a permeability of a degreasing liquid into a covering layer formed on a surface of a metal sheet by the lubricant composition. As a result, it becomes easy to peel off the covering layer from the surface of the metal sheet, and the degreasing property of the lubricant composition is improved.

Examples for the polyoxyethylene alkyl ether may include polyoxyethylene lauryl ethers, polyoxyethylene cetyl ethers, polyoxyethylene stearyl ethers, polyoxyethylene oleyl ethers, polyoxyethylene behenyl ethers, polyoxyethylene branched alkyl ethers, etc. Among them, polyoxyethylene stearyl ethers and polyoxyethylene branched alkyl ethers are preferred, and polyoxyethylene stearyl ethers are more preferred. When the polyoxyethylene alkyl ether is such a compound, the permeation of a degreasing liquid into the lubricant composition is promoted, and the degreasing property of the lubricant composition is further improved.

A lower limit of the HLB value of the polyoxyethylene alkyl ether is preferably 10, more preferably 11, and even more preferably 12. On the other hand, an upper limit of the HLB value is preferably 20, more preferably 18, and even more preferably 15. When the HLB value is smaller than the lower limit, there is a concern that the degreasing property of the lubricant composition is lowered. To the contrary, when the HLB value exceeds the upper limit, there is a concern that production cost of the lubricant composition increases.

A lower limit of a content of the polyoxyethylene alkyl ether relative to 100 parts by mass of total of the paraffin wax and the liquid paraffin is preferably 1 part by mass, and more preferably 2 parts by mass. On the other hand, an upper limit of the content is preferably 10 parts by mass, and more preferably 5 parts by mass. When the content is lower than the lower limit, there is a concern that it becomes difficult to improve the degreasing property of the lubricant composition. To the contrary, when the content exceeds the upper limit, there is a concern that the paraffin wax and the liquid paraffin are separated, or a concern that a metal sheet on which the lubricant composition is applied becomes easily rusted.

A lower limit of total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether relative to 100 parts by mass of total of the paraffin wax and the liquid paraffin is preferably 6 parts by mass, more preferably 10 parts by mass, and even more preferably 15 parts by mass. On the other hand, an upper limit of the content is preferably 40 parts by mass, more preferably 35 parts by mass, and even more preferably 30 parts by mass. When the total content is smaller than the lower limit, there is a concern that it becomes difficult to mix the paraffin wax and the liquid paraffin. To the contrary, when the total content exceeds the upper limit, there is a concern that a moldability of a metal sheet covered with the lubricant composition is lowered.

<Other Components>

Examples for other components which the lubricant composition may comprise may include a wax other than paraffin waxes, a higher fatty acid, a higher alcohol, resin fine particles, an organic peroxide, a solvent, etc.

It is also preferred that the lubricant composition comprises an inorganic acid surfactant as the other component. When the lubricant composition comprises an inorganic acid surfactant, the degreasing property and the corrosion resistance of the lubricant composition are further improved.

(Wax Other than Paraffin Waxes)

Examples for the wax other than paraffin waxes may include micro crystalline waxes, carnauba waxes, montan waxes, polyethylene waxes, derivatives thereof, etc. When the lubricant composition comprises such a wax, it is possible to further improve the moldability of a metal sheet covered with the lubricant composition. It is also possible to suitably use the lubricant composition in an electrostatic application method which will be described later.

(Higher Fatty Acid)

The higher fatty acid refers to straight-chain or branched-chain saturated or unsaturated fatty acids having a number of carbon atoms of 8 or more and 22 or less. Examples for such higher fatty acid may include decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, eicosanoic acid, oleic acid, etc. When the lubricant composition comprises such a higher fatty acid, it is possible to further improve the moldability of a metal sheet covered with the lubricant composition.

(Higher Alcohol)

The higher alcohol refers to a univalent alcohol having a number of carbon atoms of 12 or more and 22 or less which is a straight-chain or branched-chain saturated or unsaturated alcohol. Examples for such higher alcohol may include decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol, etc. When the lubricant composition comprises such a higher alcohol, it is possible to further improve the moldability of a metal sheet covered with the lubricant composition.

(Resin Fine Particles)

Examples for a resin as a main component of the resin fine particles may include amide waxes, polyethylene, polypropylene, plytetrafluoroethylene, etc. When the lubricant composition comprises such resin fine particles, it is possible to further improve the moldability of a metal sheet covered with the lubricant composition.

A lower limit of an average particle size of the resin fine particles is preferably 1 μm. On the other hand, an upper limit of the average particle size is preferably 10 μm. When the average particle size is smaller than the lower limit, there is a concern that a production cost of the resin fine particles increases. To the contrary, when the average particle size exceeds the upper limit, there is a concern that the resin fine particles easily drop out from a layer formed with the lubricant composition, and it becomes difficult to improve the moldability of a metal sheet covered with the lubricant composition. As used herein, the “average particle size” refers to a volume average particle size represented by a center diameter D50 determined by means of a laser analysis scattering method, using a particle size measuring device (for example, “LS13 320” of Beckman Coulter, Inc.).

(Organic Peroxide)

Examples for the organic peroxide may include dialkyl peroxides, and examples for the dialkyl peroxides may include di-t-butyl peroxide, t-butyl-α-cumyl peroxide, di-α-cumyl peroxide, 1,3-di(2-t-butyl peroxyisopropyl)benzene, 1,4-di(2-t-butyl peroxyisopropyl)benzene, 2,5-dimethyl-2,5-bis(t-butyl peroxy)hexane, 2,5-dimethyl-2,5-bis(t-butyl peroxy)-3-hexyne, diisopropylbenzene hydroperoxide, etc. When a metal sheet covered with the lubricant composition is subjected to a resistance spot welding, the lubricant composition is capable of maintain a welding strength, by comprising such an organic peroxide.

(Solvent)

Examples for the solvent may include water, aqueous organic solvents which are compatible with water. Examples for the aqueous organic solvents may include alcohols such as methanol, ethanol, isopropanol, butanol;

ether alcohols such as methyl cellosolve, ethyl cellosolve;

ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone;

glycols such as ethylene glycol, propylene glycol;

glycol ethers of the glycols;

glycol esters of the glycols; etc. When the lubricant comprises such a solvent, it is possible to improve stability of a coating when the lubricant composition is applied on a metal sheet. Besides, it becomes easy to apply the lubricant composition.

An upper limit of a content of the other components in the lubricant composition is preferably 10 mass %, and more preferably 8 mass %. When the content exceeds the upper limit, there is a concern that it becomes impossible to provide the degreasing property, the corrosion resistance, and the moldability of a metal sheet covered with the lubricant composition at high levels together.

A lower limit of a melting peak temperature of the lubricant composition is preferably 30° C., and more preferably 35° C. On the other hand, an upper limit of the melting peak temperature is preferably 70° C., and more preferably 60° C. When the melting peak temperature is lower than the lower limit, there is a concern that it becomes difficult to solidify the lubricant composition at a normal temperature. To the contrary, when the melting peak temperature exceeds the upper limit, there is a concein of increase of cost at the time of applying the lubricant composition on a metal sheet by means of an electrostatic application method which will be described later. As used herein, the “melting peak temperature” refers to a value determined in conformity with JIS-K7121 (2012).

A lower limit of an electrical resistance value at 90° C. of the lubricant composition is preferably 30 MΩ. When the electrical resistance value is lower than the lower limit, there is a concern that it becomes difficult to apply the lubricant composition on a metal sheet by means of an electrostatic application method which will be described later.

On the other hand, an upper limit of the electrical resistance value at 90° C. of the lubricant composition varies depending on materials which constitute an electrostatic application device. In other words, it is preferred that the electrical resistance value is equal to a specific resistivity of a high voltage applying unit of an electrostatic application device. For example, this specific resistivity of a high voltage applying unit is 1×10¹⁴ Ωcm when the high voltage applying unit comprises a resin material such as polyacetal. When the electrical resistance value exceeds the specific resistivity, there is a concern that a dielectric breakdown of the electrostatic application device occurs.

<Production Method of the Lubricant Composition>

The lubricant composition is obtained by mixing the paraffin wax, the liquid paraffin, and the sorbitan fatty acid ester, and a polyoxyethylene alkyl ether as an optional component, at a predetermined proportion.

<Advantage>

By comprising the paraffin wax and the liquid paraffin at the above described proportion, the lubricant composition improves a friction reducing effect at the time of pressing, and as a result, improves the moldability of a metal sheet covered with the lubricant composition. In addition, the degreasing property by alkali of the lubricant composition is also improved. Furthermore, by comprising the sorbitan fatty acid ester having an HLB value in the above described range at the above described proportion, the lubricant composition is capable of improving the corrosion resistance thereof, due to a low hydrophilicity of the sorbitan fatty acid ester.

[Lubricant Composition-Covered Metal Sheet]

The lubricant composition-covered metal sheet comprises a metal sheet and a lubricant layer laminated on at least one of the faces of the metal sheet.

<Metal Sheet>

A metal as a main component of the metal sheet is not particularly limited, and examples therefor may include aluminum, aluminum alloys, steel, copper, titanium, etc. Among them, aluminum and aluminum alloys are preferred, and aluminum alloys are more preferred.

The lubricant layer is formed with the lubricant composition, and laminated on at least one of the faces of the metal sheet. A lower limit of an average thickness of the lubricant layer is preferably 0.1 μm, and more preferably 0.5 μm. On the other hand, an upper limit of the average thickness is preferably 10 μm, and more preferably 8 μm. When the average thickness is lower than the lower limit, there is a concern that a moldability of a metal sheet covered with the lubricant composition is lowered. To the contrary, when the average thickness exceeds the upper limit, there is a concern that a degreasing property by alkali is lowered, or a concern that production cost increases.

A lower limit of an amount of deposition of the lubricant composition which forms the lubricant layer on one of the faces of the metal sheet is preferably 0.2 g/m², and more preferably 0.5 g/m². On the other hand, an upper limit of the amount of deposition is preferably 2.0 g/m², and more preferably 1.2 g/m². When the amount of deposition is lower than the lower limit, there is a concern that a moldability of a metal sheet covered with the lubricant composition is lowered. To the contrary, when the amount of deposition exceeds the upper limit, there is a concern that a degreasing property by alkali is lowered, or a concern that a production cost increases.

<Production Method of the Lubricant Composition-Covered Metal Sheet>

Examples for production method of the lubricant composition-covered metal sheet may include methods comprising a step of forming a covering layer on a surface of a metal sheet by using the lubricant composition by means of a paint method, an electrostatic application method or the like. Among them, it is preferred to use, in the step, the electrostatic application method of low cost with low environmental load, which is capable of easily forming a uniform covering layer.

In a case of producing the lubricant composition-covered metal sheet by means of the paint method, the lubricant composition is dissolved or dispersed in an organic solvent such as xylene or toluene, and the solution or the dispersion liquid is applied on a surface of a metal sheet by using a bar coater, a roll coater, a spray or the like, to form a coating. Subsequently, the coating is heated to remove the solvent therein, to thus obtain the lubricant composition-covered metal sheet.

In the case of producing the lubricant composition-covered metal sheet by means of the paint method, a lower limit of a concentration of a solution of the lubricant composition dissolved in an organic solvent, or of a dispersion liquid of the lubricant composition dispersed in an organic solvent is preferably 20 mass %, and more preferably 30 mass %. On the other hand, an upper limit of the concentration is preferably 70 mass %, and more preferably 60 mass %. When the concentration is lower than the lower limit, there is a concern that a removal of the solvent in the coating requires a long time heating, resulting an increase of production cost of the lubricant composition-covered metal sheet. To the contrary, when the concentration exceeds the upper limit, there is a concern that it becomes difficult to uniformly apply the lubricant composition on a metal sheet.

In a case of producing the lubricant composition-covered metal sheet by means of the electrostatic application method, the lubricant composition is heated up to a temperature higher than the melting point thereof, and applied on a surface of a metal sheet by means of the electrostatic application method. Subsequently, the metal sheet on which the lubricant composition is applied is cooled, to thus obtain the lubricant composition-covered metal sheet.

The electrostatic application method is capable of uniformly and efficiently applying the lubricant composition on a metal sheet at a high speed. In addition, since it is possible to form a solid covering layer only by cooling the lubricant composition after applied, the method does not need the heating for removal of the solvent, which was essential in the paint method. Therefore, it is possible to significantly reduce an amount of energy used in the production, allowing a cost down and a reduction of environmental load.

A lower limit of the heating temperature in the electrostatic application method is preferably 70° C., and more preferably 75° C. On the other hand, an upper limit of the heating temperature is preferably 100° C., and more preferably 95° C. When the heating temperature is lower than the lower limit, there is a concern that application of the lubricant composition becomes difficult. To the contrary, when the heating temperature exceeds the upper limit, there is a concern that the lubricant composition is deteriorated.

A lower limit of an applied voltage in the electrostatic application method is preferably −100 kV, and more preferably −80 kV. On the other hand, an upper limit of the applied voltage is preferably −50 kV, and more preferably −60 kV. When the applied voltage is smaller than the lower limit, there is a concern that production cost of the lubricant composition-covered metal sheet increases. To the contrary, when the applied voltage exceeds the upper limit, there is a concern that the application of the lubricant composition becomes difficult.

<Advantage>

For using the lubricant composition, the lubricant composition-covered metal sheet is excellent in degreasing property and corrosion resistance, and at the same time, excellent in moldability at the time of pressing.

[Other Embodiments]

The lubricant composition and the lubricant composition-covered metal sheet of the present invention are not limited to the embodiments described above. For example, the lubricant composition may be applied either on only one of the faces, or on both faces of a metal sheet. Furthermore, the lubricant composition may be applied either on the entire surface, or only on a region where a pressure is applied at a time of pressing, of one of the faces or both faces of a metal sheet.

EXAMPLES

Hereinbelow, the present invention will be described more concretely by way of examples to which the present invention is not limited.

Example 1

A lubricant composition was prepared by mixing 28 parts by mass of the paraffin wax (A-1), 56 parts by mass of the liquid paraffin (B-1), 13 parts by mass of the sorbitan fatty acid ester (C-1), and 3 parts by mass of the polyoxyethylene alkyl ether (D-1) which are shown below.

Examples 2 to 15 and Comparative Examples 1 to 12

A lubricant composition was prepared in the same manner as in Example 1 except that kinds and contents of the used substances were as in Table 1 and Table 2. Details of each component used in the Examples and the Comparative Examples are shown below.

<Paraffin Wax>

A-1: Paraffin wax PW115 (Nippon Seiro Co., Ltd.; Melting point: 48° C.) B-1: Paraffin wax PW135 (Nippon Seiro Co., Ltd.; Melting point: 59° C.)

<Liquid Paraffin>

B-1: MORESCO WHITE P-150 (Registered trademark; MORESCO Corporation; Density: 0.857 g/cm³; Kinematic viscosity at 40° C.; 30.11 mm²/s; Molecular weight: 409) B-2: MORESCO WHITE P-260 (Registered trademark; MORESCO Corporation; Density: 0.864 g/cm³; Kinematic viscosity at 40° C.; 50.7 mm²/s; Molecular weight: 453)

<Sorbitan Fatty Acid Ester>

C-1: Sorbitan trioleate (“RHEODOL SP-O30V (Registered trademark)” of Kao Chemicals Corp.; HLB value: 1.8) C-2: Sorbitan monopalmitate (“RHEODOL SP-P10 (Registered trademark)” of Kao Chemicals Corp.; HLB value: 6.7; Melting point: 46° C.) C-3: Sorbitan monostearate (“RHEODOL SP-S10V (Registered trademark)” of Kao Chemicals Corp.; HLB value: 4.7; Melting point: 51.5° C.)

<Polyoxyethylene Alkyl Ether>

D-1: Polyoxyethylene alkyl ether (“EMULGEN 709 (Registered trademark)” of Kao Chemicals Corp.; HLB value: 13.3) D-2: Polyoxyethylene stearyl ether (“EMULGEN 320P (Registered trademark)” of Kao Chemicals Corp.; HLB value: 13.9)

<Rust Preventive Oil for Pressing> “R303PX2” of Sugimura Chemical

Incidentally, in Table 1 and Table 2, the numerical values described in ( ) represent contents when a total content of the paraffin wax and the liquid paraffin is 100 parts by mass.

TABLE 1 Polyoxyethylene Paraffin wax Liquid paraffin Sorbitan fatty acid ester alkyl ether Rust preventive A-1 A-2 B-1 B-2 C-1 C-2 C-3 D-1 D-2 oil for pressing Content Content Content Content Content Content Content Content Content Content (part by (part by (part by (part by (part by (part by (part by (part by (part by (part by mass) mass) mass) mass) mass) mass) mass) mass) mass) mass) Example 1 28 — 56 — 13 (15.5) — — 3 (3.6) — — Example 2 56 — 28 — 13 (15.5) — — 3 (3.6) — — Example 3 42 — 42 — 13 (15.5) — — 3 (3.6) — — Example 4 29 — 56 — 14 (16.5) — — — — — Example 5 56 — — 28 13 (15.5) — — 3 (3.6) — — Example 6 42 — — 42 13 (15.5) — — 3 (3.6) — — Example 7 28 — — 56 15 (17.9) — — — — — Example 8 38 — — 38 20 (26.3) — — 5 (6.6) — — Example 9 44 — — 31 20 (26.7) — — 5 (6.7) — — Example 10 45 — — 45 8 (8.9) — — 2 (2.2) — — Example 11 54 — — 36 8 (8.9) — — 2 (2.2) — — Example 12 40 — — 40 16 (20)   — — 4 (5)   — — Example 13 47 — — 33 16 (20)   — — 4 (5)   — — Example 14 49 — — 35 13 (15.5) — — 3 (3.6) — — Example 15 28 — — 56 13 (15.5) — — 3 (3.6) — —

TABLE 2 Polyoxyethylene Paraffin wax Liquid paraffin Sorbitan fatty acid ester alkyl ether Rust preventive A-1 A-2 B-1 B-2 C-1 C-2 C-3 D-1 D-2 oil for pressing Content Content Content Content Content Content Content Content Content Content (part by (part by (part by (part by (part by (part by (part by (part by (part by (part by mass) mass) mass) mass) mass) mass) mass) mass) mass) mass) Comparative 85 — — — 13 (15.3) — — 3 (3.5) — — Example 1 Comparative — — 85 — 13 (15.3) — — 3 (3.5) — — Example 2 Comparative — — — 85 13 (15.3) — — 3 (3.5) — — Example 3 Comparative 42 — — 42 — 13 (15.5) — 3 (3.6) — — Example 4 Comparative 49 — — 35 — 13 (15.5) — 3 (3.6) — — Example 5 Comparative 42 — — 42 — — 13 (15.5) 3 (3.6) — — Example 6 Comparative 49 — — 35 — — 13 (15.5) 3 (3.6) — — Example 7 Comparative 29 — 57 — — — — 14 (16.7) — — Example 8 Comparative 28 — — 56 — — — 15 (17.9) — — Example 9 Comparative — 14 — 56 — — — — 30 (42.9) — Example 10 Comparative — 16 — 64 — — — — 20 (25)   — Example 11 Comparative — — — — — — — — — 100 Example 12

<Evaluation>

The lubricant compositions of the Examples and the Comparative Examples were evaluated in the following process.

(Degreasing Property)

6000 series aluminum alloy sheets having an average thickness of 1 mm, a length of 100 mm and a width of 100 mm were degreased, and on one of the faces of each, a lubricant composition of Examples and Comparative Examples was applied such that a deposition amount is 1.0 g/m², by means of an electrostatic application method, to thus obtain lubricant composition-covered metal sheets. These lubricant composition-covered metal sheets were dipped in an alkaline washing solution (“Surf Cleaner EC90” of Nippon Paint Co., Ltd.; pH: 11 to 12) by three sheets for two minutes, which were then washed with water for 1 minute. Surfaces of the lubricant composition-covered metal sheets after washed with water were observed visually, and evaluated on the basis of the following standards. Results of the evaluation are shown in Table 3.

A: Almost entire of a surface was wet with water and completely degreased. B: A surface had a small number of cissings or drops remained thereon, and was almost degreased. C. A surface obviously had a large number of cissings or drops, and was degreased insufficiently.

(Corrosion Resistance)

A NaCl solution of 5 mass % was uniformly sprayed on lubricant composition-covered metal sheets of the same size with those used in the above evaluation of degreasing property, which were then kept at a temperature of 40° C. in a relative humidity of 70% for one night. After that, surfaces of the lubricant composition-covered metal sheets were observed visually, and evaluated on the basis of the following standards. Results of the evaluation are shown in Table 3.

A: A surface was not changed in color, and excellent in corrosion resistance. B: A surface had a few white dots, and was a little inferior in corrosion resistance. C. A surface obviously had numerous white dots, and was inferior in corrosion resistance.

(Moldability)

6000 series aluminum alloy sheets having an average thickness of 1mm, a length of 110 mm and a width of 180 mm were degreased, and on both faces of each, a lubricant composition of the Examples and the Comparative Examples was applied such that a deposition amount is 1.0 g/m², by means of an electrostatic application method, to thus obtain lubricant composition-covered metal sheets. Outer peripheries of these lubricant composition-covered metal sheets were held by using lock beads with a blank holder force of 200 kN. Subsequently, the lubricant composition-covered metal sheets were subjected to a stretch forming until they were ruptured, by use of a 80 ton hydraulic press (“1M080L” of AMINO Inc.) at a pressing speed of 4 mm/s, using a hemispherical punch having a diameter of 50.8 mmφ. This stretch forming was conducted three times for each, and an average value of formed heights at the rupture was represented by LDH (mm). This LDH was evaluated on the basis of the following standards. Results of the evaluation are shown in Table 3.

A: LDH was 35 mm or more, and the moldability was excellent. C: LDH was less than 35 mm, and the moldability was insufficient.

TABLE 3 Degreasing Corrosion property resistance moldability Example 1 A A A Example 2 B A A Example 3 A A A Example 4 B A A Example 5 B A A Example 6 A A A Example 7 B A A Example 8 B A A Example 9 B A A Example 10 B A A Example 11 B A A Example 12 A A A Example 13 A A A Example 14 A A A Example 15 A A A Comparative Example 1 C A A Comparative Example 2 A A C Comparative Example 3 A A C Comparative Example 4 C C A Comparative Example 5 C C A Comparative Example 6 C C A Comparative Example 7 C C A Comparative Example 8 A C A Comparative Example 9 A C A Comparative Example 10 B C A Comparative Example 11 C C A Comparative Example 12 A A C

As shown in Table 3, the lubricant compositions of the Examples were excellent in degreasing property, corrosion resistance, and in moldability of a metal sheet covered with the lubricant composition, and in particular, extremely excellent in the corrosion resistance and the moldability among all the Examples.

Example 1 and Example 4 had the same combination of components, except for the polyoxyethylene alkyl ether, and contents of the components were approximate. Example 1 comprising the polyoxyethylene alkyl ether was superior in degreasing property to Example 4 which did not comprise the polyoxyethylene alkyl ether. Similarly, Example 7 and Example 15 had the same combination of components, except for the polyoxyethylene alkyl ether, and contents of the components were approximate. Example 15 comprising the polyoxyethylene alkyl ether was superior in degreasing property to Example 7 which did not comprise the polyoxyethylene alkyl ether.

Furthermore, Examples 8 to 11 and Examples 12 to 14 had the same combination of components, except for total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether relative to 100 parts by mass of the paraffin wax and the liquid paraffin, and contents of the components were approximate. Examples 12 to 14 having the total content of 15 parts by mass or more and 30 parts by mass or less was superior in degreasing property to Examples 8 and 9 having the total content of more than 30 parts by mass and to Examples 10 and 11 having the total content of less than 15 parts by mass.

In addition, Examples 1 to 3 had the same combination of components, except for content of the liquid paraffin relative to 100 parts by mass of the paraffin wax, and contents of the components were approximate. Examples 1 and 3 having the content of the liquid paraffin of more than 50 parts by mass were superior in degreasing property to Example 2 having the content of the liquid paraffin of 50 parts by mass. Similarly, Examples 5, 6, 14 and 15 had the same combination of components, except for content of the liquid paraffin relative to 100 parts by mass of the paraffin wax, and contents of the components were approximate. Examples 6, 14 and 15 having the content of the liquid paraffin of more than 50 parts by mass were superior in degreasing property to Example 5 having the content of 50 parts by mass.

On the other hand, the lubricant compositions of the Comparative Examples did not have the degreasing property, the corrosion resistance and the moldability of a metal sheet covered with the lubricant composition together, and many of the lubricant compositions were inferior especially in the degreasing property and the corrosion resistance. Comparative Examples 5 to 8, in which HLB values of sorbitan fatty acid ester were more than 4.5 were significantly inferior in both the degreasing property and the corrosion resistance. Furthermore, the Comparative Example 12, in which a conventional lubricant oil was used was inferior in the moldability of a metal sheet, although excellent in the degreasing property and the corrosion resistance.

INDUSTRIAL APPLICABILITY

As described above, the lubricant composition and the lubricant composition-covered metal sheet of the present invention are excellent in degreasing property, corrosion resistance, and in moldability of a metal sheet covered with the lubricant composition. Therefore, a use of the lubricant composition of the present invention allows diversified presswork of a metal sheet. 

1. A lubricant composition comprising a paraffin wax, a liquid paraffin, and a sorbitan fatty acid ester, wherein a content of the liquid paraffin relative to 100 parts by mass of the paraffin wax is 10 parts by mass or more and 500 parts by mass or less, an HLB value of the sorbitan fatty acid ester is more than 0 and 4.5 or less, and a content of the sorbitan fatty acid ester relative to 100 parts by mass of a total of the paraffin wax and the liquid paraffin is 5 parts by mass or more and 30 parts by mass or less.
 2. The lubricant composition according to claim 1, wherein the sorbitan fatty acid ester is one comprising a sorbitan having only a part of hydroxyl groups thereof esterified.
 3. The lubricant composition according to claim 1, further comprising a polyoxyethylene alkyl ether, with an HLB value of the polyoxyethylene alkyl ether being 10 or more and 20 or less.
 4. The lubricant composition according to claim 3, wherein a total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether relative to 100 parts by mass of a total of the paraffin wax and the liquid paraffin is 5 parts by mass or more and 40 parts by mass or less.
 5. The lubricant composition according to claim 2, further comprising a polyoxyethylene alkyl ether, with an HLB value of the polyoxyethylene alkyl ether being 10 or more and 20 or less.
 6. The lubricant composition according to claim 5, wherein a total content of the sorbitan fatty acid ester and the polyoxyethylene alkyl ether relative to 100 parts by mass of a total of the paraffin wax and the liquid paraffin is 5 parts by mass or more and 40 parts by mass or less.
 7. The lubricant composition according to claim 1, wherein a melting point determined in conformity with JIS-K2235 (2009) of the paraffin wax is 45° C. or higher and 65° C. or lower.
 8. The lubricant composition according to claim 1, wherein a molecular weight of the liquid paraffin is larger than a molecular weight of the paraffin wax, and a difference between the molecular weight of the liquid paraffin and the molecular weight of the paraffin wax is 50 or more and 200 or less.
 9. A lubricant composition-covered metal sheet, comprising a metal sheet and a lubricant layer laminated at least on one of the faces of the metal sheet, wherein the lubricant layer is formed with the lubricant composition according to claim
 1. 